A lot of races and classes have abilities that can either be used proficiency bonus times per long rest, or that can be used once per short or long rest.
For evaluating homebrew races, you often need to compare abilities, and sometimes while the effects are similar, the difference is the formula ...
And I'm thinking a minecart battle. A series of strength checks to apply the brakes/control speed; dex checks to unhook extra minecarts in the train/avoid enemy arrows...
I like the idea of an encounter where characters can fall off and be left behind, and the enemies can get away if all of the players fall off or stop giving chase.
@AncientSwordRage They wait for the encounter to be over. Ideally, the encounter isn't a long one.
Something like 2-3 rounds, tops.
And ideally, everyone gets at least one round of action
"I cast Fireball and then get knocked off my cart." "I land two attacks with my Greatsword and manage to leap to the next cart." etc.
It's like a Save or Die, but limited to just the encounter.
And then there's an opportunity for the characters to RP it out, like the Wizard being upside down in a pile of crates, the Barbarian leaving an impact silhouette in a wall, etc.
Or, if they're really tenacious and they find a way to catch up, like summoning a Horse with Phantom Steed, or something.